1. Field of the Invention
The present invention relates generally to systems and methods for detecting moisture ingress, and more particularly, to systems and methods for detecting water and ice accumulation on an aircraft.
2. Related Art
The use of air travel has greatly increased in recent decades to the point that it is today a common form of transportation. As such, there is an ever present need to increase the safety, efficiency, and environmental impact of modern aircraft.
Generally, transport type commercial, military, and some private aircraft fly through environmentally hostile environments that typically lead to water accumulation in these types of aircraft. Specifically, transport carrying aircraft typically have moisture-related problems that include ice formation within the airframe of the aircraft, water dripping onto passengers within the passenger cabin, water accumulation in the airframe, electrical equipment failures, and wet insulation blankets within the airframe of the aircraft. Generally, the extent of these problems will vary among aircraft operators and among individual aircraft depending on how they are utilized; however, even taking these factors into account, all transport aircraft will experience some type of moisture-related problems.
Specifically, all commercial aircraft that carry passengers will experience moisture-related problems in service because the chief source of moisture inside these aircraft is passenger respiration and the resulting condensation (or freezing) of this moisture on the skin of the aircraft. Additionally, there may be water ingress (i.e., moisture from the external environment of the aircraft) into the aircraft while the aircraft is on the ground before takeoff. This combined moisture (i.e., from both respiration and water ingress) may condense along the airframe while the aircraft is in flight.
Typically, this type of condensation on the airframe of an aircraft occurs during flight when the temperature of both the outside air and the airframe are very cold. It is appreciated by those skilled in the art that the atmospheric air temperature drops relative to geometric altitude. Specifically, Tables 1 and 2 provide the highest and lowest temperature ever recorded as function of geometric altitude based on MIL-HDBK-310 (from the Military Handbook: Global Climatic Data For Developing Military Products (23 Jun. 1997)). The airplane is operating within this environment envelope. Depending on airplane model, the temperature at the skin of the airplane is varied and it is greatly dependent on operational altitude and cruising speed.
TABLE 1Highest Recorded Temperature as a Function of Geometric AltitudePRESSUREGEOMETRIC ALTITUDEALT.ALTITUDETEMPDENSITYTEMP(km)(kft)(° C.)(° F.)(kg/m3)(lb/ft3)(° C.)(° F.)00581361052 × 10−3657 × 10−4——13.284110610186364010426.5632909165723188413.119667624761966619.7846611381643826.2−425499312−4251032.8−139393245−1801239.4−22−8316197−27−171445.9−30−22208130−34−291652.5−35−3115697−35−311859.1−35−3111874−34−292065.6−31−248654−31−242272.2−29−206440−31−242478.7−33−274830−31−242085.3−27−173622−27−172891.9−22−82717−22−83098.4−1712012−170
TABLE 2Lowest Recorded Temperature as a Function of Geometric AltitudePRESSUREGEOMETRIC ALTITUDEALT.ALTITUDETEMPDENSITYTEMP(km)(kft)(° C.)(° F.)(kg/m3)(lb/ft3)(° C.)(° F.)00−68−901780 × 10−31111 × 10−4——13.28−54−651419886−56−6926.56−47−531147716−47−53413.1−53−63899561−51−60619.7−61−78681425−60−76826.2−68−90510318−64−831032.8−75−103409255−73−991239.4−80−112314196−77−1071445.9−77−107218136−78−1081652.5−87−125208130−87−1251859.1−88−12614389−85−1212065.6−87−1257849−83−1172272.2−85−1215434−85−1212478.7−86−1233824−85−1212085.3−84−1192918−85−1212891.9−84−1192012−85−1213098.4−85−121116.9−85−121
As such, the airframe temperatures are usually below the dew point of the air in the passenger cabin of the aircraft, causing some amount of condensation to form during most flights from the water vapor in the moist air inside the aircraft. This condensation results when the moist air in the passenger cabin moves to the cold airframe. The cabin air passes through small gaps in the insulation coverage between the inner surfaces of the airframe and outer skin of the airframe and then cools rapidly when it comes in contact with the inside surface of the outer skin of the airframe.
Buoyancy forces typically induce a continuous flow of air and continuous movement of moisture to the cold airframe. Usually, the rate of condensation depends on the rate of buoyancy-driven air movement to the airframe as well as the cabin humidity level. The in-flight cabin humidity levels are low from a standpoint of human comfort (i.e., usually less than 20 percent relative humidity); however, the cabin air is not completely dry, and any moisture it contains will condense as the cabin air moves over the cold airframe. In addition, because the airframe temperatures in flight are normally below the freezing point of water, most of the condensed water vapor from the cabin air will freeze to form ice in the form of frost, which typically accumulates along some of the inner surfaces of the airframe such as, for example, the inside surface of the outer skin of the airframe.
Once the aircraft descends and finally lands, the frost or ice melts rapidly if the conditions allow the aircraft skin temperature to rise above freezing. This typically causes a sudden onset of drainage fluid as the ice melts, which, if not managed completely, drips into the crown area (i.e., the attic) of the aircraft (and possibly into the passenger cabin), and other enclosed spaces of the airframe. Once condensed and unfrozen, the liquid water accumulates within the airframe in different enclosed spaces or in the insulation blankets used to insulate the inner surfaces of the airframe from the outer skin. This process may repeat itself many times as the aircraft travels back and forth between destinations resulting in cyclic loading to the airframe structure and/or various electrical systems in the aircraft.
In general, these condensation conditions and the resulting moisture problems are influenced heavily by seating density and aircraft operations, especially load factors and utilization rates. High passenger loads result in higher cabin humidity and higher condensation rates. High aircraft-utilization rates result in more time during which the airframe is below the dew point or frost point and greater accumulations of frost and water on a daily basis. Generally, some of the most severe moisture problems occur on aircraft with combinations of high seating density, high load factors, and high utilization rates.
In order to better illustrate the above discussion, in FIG. 1, a front cross-sectional view of a known aircraft 100 is shown. The aircraft 100 is shown to have an airframe structure that includes a fuselage 102 and a pair of wings 104. The fuselage 102 includes an outer fuselage skin 106, an inner fuselage skin 108 (which may also be referred to as an inner fuselage sidewall 108), and a door 110. Insulation blanket material 112 is located between the outer fuselage skin 106 and the inner fuselage skin 108. The outer fuselage skin 106 is in contact with the outside environment 114 and the inner fuselage skin 108 is in contact with the inside environment 116. The inside environment 116 includes a plurality of passenger seats 118 located within a passenger cabin.
When water vapor 120 enters the inside environment 116 of the aircraft via water ingress from outside the door 110 or from respiration of passengers sitting in the passenger seats 118, it typically travels along different parts of the inside environment 116 and comes in contact with the inner fuselage skin 108. Assuming that there is an insulation blanket material 112 located between the outer fuselage skin 106 and the inner fuselage skin 108, the water vapor 120 typically passes through the inner fuselage skin 108 and insulation blanket material 112 to the outer fuselage skin 106.
Unfortunately, when the aircraft is in flight at a high enough altitude and the water vapor 120 comes in contact with the outer fuselage skin 106, the water vapor 118 will immediately condense into water that may freeze into ice 122 (i.e., frost) on the inside of the outer fuselage skin 106. Once the aircraft descends to a low enough altitude and/or lands, the ice 122 may melt and drain 124 along the inside of the outer fuselage skin 106 to form an accumulation of water 126 somewhat along the inside of the outer fuselage skin 106. Similarly, some of water vapor 120 may not actually freeze into ice and will simply condense into liquid water that will also drain 124 along the inside of the outer fuselage skin 106 to add to the accumulation of water 126. It is appreciated that as some of the liquid water drains 124 along the inside of the outer fuselage skin 106 it will be absorbed (not shown) by the insulation blanket material 112.
It is appreciated the path of drainage 124 is an example path and that draining water may take multiple paths throughout the airframe 100 to reach the pool of accumulated water 126. As another example, the melted water from the ice 122 may drain 128 to the pool of accumulated water 126 through part of insulating blanket material 112 inside of the outer fuselage skin 106 until it reaches the floor board 130 of the passenger cabin. Once it reaches the cabin floor board 130, it may drain 128 along the cabin floor board 130 until it finds an opening in the cabin floor board 130 where it then drips 134 to the pool of accumulated water 126.
If the insulation blanket material 112 is faulty because it has absorbed enough water so that it no longer functions properly in thermally insulating the outer fuselage skin 106 from the inner fuselage skin 108, such that the inner fuselage skin 108 is maintained at a below freezing temperature, the water vapor 118 may also freeze along the inner fuselage skin 108 and consequently form ice accumulation (i.e., frost) and accumulation of water (not shown) along the inner fuselage skin 108 similar to the ice 120 accumulation along the inside of the outer fuselage skin 106 and accumulation of water 124 somewhat along the inside of the outer fuselage skin 106.
This accumulation of ice and water typically leads to damage of the aircraft structure and/or systems, increased weight of the aircraft (caused by the increased water weight), and discomfort of the passengers within the aircraft. Specifically, ice accumulation within the aircraft structure may cause problems or even failure to mechanical movement of mechanical systems such as, on the less dangerous side, a roller shade assembly of a window shade, possible breakdown of the insulation material between the outer and inner fuselage skin of the aircraft, to problems with the landing gear or control surfaces of the aircraft. Water accumulation within the aircraft structure may cause problems that include increased humidity and possible water leakage (i.e., dripping) within the passenger compartment of the aircraft leading to passenger discomfort and reduced passenger satisfaction within the aircraft, increased weight of the aircraft (which leads to greater fuel consumption), accumulation of water in the cargo bay area of the aircraft, accumulation of water in the air conditioning ducts within the aircraft, corrosion of parts of the aircraft structure, corrosion and subsequent failure of electrical wiring within the aircraft, and short circuitry of onboard electrical system. As such, there is a need for a system and method for detecting and quantitatively assessing any water ingress and accumulation of ice and water in an aircraft.